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Why Dryness Cracks Instruments

Wood absorbs moisture from humid air and looses moisture to dry air. Cold air holds less humidity than warm air. When temperatures drop, the amount of water vapor in the air also drops. While a furnace or fireplace can warm the air, it does nothing to increase the humidity in it. The dry air circulating in your home dries everything in it. The wood in your stringed instruments shrink.


Each wood shrinks a uniquely as it dries. Soft woods like spruce and cedar shrink more than hardwoods like maple, mahogany and rosewood. Because the top of stringed instruments are usually spruce or cedar, and the backs are always hardwoods, the tops of the instruments shrink more than the backs and sides. Glued to the backs and sides, the tops cannot shrink as much as they would if they were not fastened to a comparatively immobile hardwood. The tops crack to relieve the stresses caused by the dissimilar amount of shrinking. 


The cracks can be repaired, but it costs you money and you are without your instrument while it is in the shop for repair. Often, the repair is visible. Even when it is invisible, it damages the monetary value of the instrument. Put simply, it is superior to prevent a crack than to repair one.


The best way to prevent cracking is to maintain the relative humidity in the room where the instrument 'lives' at 40-45%. Some people do it with humidifiers in their heating systems. Others use console models like the ones that Aircare and Kenmore make. Some people use ionic humidifiers like those made by Boneco (formerly Air-O-Swiss).


Another way to maintain humidity is with an in-case humidifier. This approach works well if you prefer not to run a humidifier in your home or if you have to take your instrument out of your home often. Our favorite styles are made by Planet Waves and Stretto.


The long-and-short of it is that you should do SOMETHING to maintain humidity at 40% or above so that you don't end up with a cracked instrument. In SE Pennsylvania, we normally need to humidify from November first through the middle or end of April. We encourage you to spend a little time and money on maintaining humidity so that you don't have to spend a lot on repairs.


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